# [sdiy] Techniques for Multiplying MIDI Clock frequency?

Pete Hartman pete.hartman at gmail.com
Sat Dec 18 22:10:46 CET 2021

```Right but where the divisions are going to fall when you're doing an odd
divisor that includes a factor of 3 is going to shift around if the pulses
being divided aren't evenly spaced.

I tried to make an ASCII representation to verify this expectation:

|   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|   |   |   |   |   |   |   |   |   |   |   |   |      Original pulse train
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | | | | | | | |    evenly divided
|     |     |     |     |     |     |     |     |     |     |     |     |
|     |     |     |     |     |     |     |     |    divide by 3
||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||
||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||  ||     unevenly divided
|    |      |    |      |    |      |    |      |    |      |    |      |
|      |    |      |    |      |    |      |    |     divide by 3
|     |     |     |     |     |     |     |     |     |     |     |     |
|     |     |     |     |     |     |     |     |    the even div/3 for
comparison

Hopefully everyone's email clients can cope with the monospace required to
make this obvious.

On Sat, Dec 18, 2021 at 3:00 PM Benjamin Tremblay <btremblay at mac.com> wrote:

> If I’m waiting around doing nothing until I count 12 pulses, all that
> matters is I construct a square wave 12 pulses long.
>
> Benjamin Tremblay
>
> On Dec 18, 2021, at 3:56 PM, Benjamin Tremblay <btremblay at me.com> wrote:
>
> ﻿I’m assuming all it does is divide by 12 to get a 16th note.
>
> Benjamin Tremblay
>
> On Dec 18, 2021, at 3:53 PM, Pete Hartman <pete.hartman at gmail.com> wrote:
>
> ﻿
>
>
> On Sat, Dec 18, 2021 at 2:15 PM Benjamin Tremblay via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
>>
>> 2) I wish I understood the theory of clock multipliers. I have seen code
>> that measures the period between clock pulses and dead reckons the
>> double-time pulse as an average of the recent periods. But why? Why can’t I
>> just fire another extra HIGH-LOW pulse whenever I get a MIDI clock event?
>> Why does timing of the extra ticks matter?  I’m assuming 48 PPQ divides the
>> clock down to individual sequencer steps on the KPR-77. As long as the
>> divided clock is coming in on the beat, what does it matter if some of the
>> synthetic pulses are a little off? (They’re just shadows of the main tempo
>> clock). It’s not like the KPR-77 is inferring something or trying to
>> calculate BPM from the external clock… So… Anyway I just wish I knew what I
>> was aiming for, and then maybe I could hit the target.
>>
>
> One suspects that most people are trying to write a general purpose
> converter.  E.g. you could run those 48ppq out to some other module, like
> an analog sequencer, and it would keep time.  I'm not familiar with the
> KPR-77, but I'm also slightly puzzled by the idea that some piece of gear
> would require 48PPQN but not care about the timing of half of the pulses.
>
> Pete
>
>
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